locking/Documentation: Move locking related docs into Documentation/locking/

Specifically:
  Documentation/locking/lockdep-design.txt
  Documentation/locking/lockstat.txt
  Documentation/locking/mutex-design.txt
  Documentation/locking/rt-mutex-design.txt
  Documentation/locking/rt-mutex.txt
  Documentation/locking/spinlocks.txt
  Documentation/locking/ww-mutex-design.txt

Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: jason.low2@hp.com
Cc: aswin@hp.com
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Mason <clm@fb.com>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Davidlohr Bueso <davidlohr@hp.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Jason Low <jason.low2@hp.com>
Cc: Josef Bacik <jbacik@fusionio.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Lubomir Rintel <lkundrak@v3.sk>
Cc: Masanari Iida <standby24x7@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: fengguang.wu@intel.com
Link: http://lkml.kernel.org/r/1406752916-3341-6-git-send-email-davidlohr@hp.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 0 insertions, 167 deletions

diff --git a/Documentation/spinlocks.txt b/Documentation/spinlocks.txt
deleted file mode 100644
index 97eaf5727178..000000000000
--- a/Documentation/spinlocks.txt
+++ /dev/null
@@ -1,167 +0,0 @@
-Lesson 1: Spin locks
-
-The most basic primitive for locking is spinlock.
-
-static DEFINE_SPINLOCK(xxx_lock);
-
-	unsigned long flags;
-
-	spin_lock_irqsave(&xxx_lock, flags);
-	... critical section here ..
-	spin_unlock_irqrestore(&xxx_lock, flags);
-
-The above is always safe. It will disable interrupts _locally_, but the
-spinlock itself will guarantee the global lock, so it will guarantee that
-there is only one thread-of-control within the region(s) protected by that
-lock. This works well even under UP also, so the code does _not_ need to
-worry about UP vs SMP issues: the spinlocks work correctly under both.
-
-   NOTE! Implications of spin_locks for memory are further described in:
-
-     Documentation/memory-barriers.txt
-       (5) LOCK operations.
-       (6) UNLOCK operations.
-
-The above is usually pretty simple (you usually need and want only one
-spinlock for most things - using more than one spinlock can make things a
-lot more complex and even slower and is usually worth it only for
-sequences that you _know_ need to be split up: avoid it at all cost if you
-aren't sure).
-
-This is really the only really hard part about spinlocks: once you start
-using spinlocks they tend to expand to areas you might not have noticed
-before, because you have to make sure the spinlocks correctly protect the
-shared data structures _everywhere_ they are used. The spinlocks are most
-easily added to places that are completely independent of other code (for
-example, internal driver data structures that nobody else ever touches).
-
-   NOTE! The spin-lock is safe only when you _also_ use the lock itself
-   to do locking across CPU's, which implies that EVERYTHING that
-   touches a shared variable has to agree about the spinlock they want
-   to use.
-
-----
-
-Lesson 2: reader-writer spinlocks.
-
-If your data accesses have a very natural pattern where you usually tend
-to mostly read from the shared variables, the reader-writer locks
-(rw_lock) versions of the spinlocks are sometimes useful. They allow multiple
-readers to be in the same critical region at once, but if somebody wants
-to change the variables it has to get an exclusive write lock.
-
-   NOTE! reader-writer locks require more atomic memory operations than
-   simple spinlocks.  Unless the reader critical section is long, you
-   are better off just using spinlocks.
-
-The routines look the same as above:
-
-   rwlock_t xxx_lock = __RW_LOCK_UNLOCKED(xxx_lock);
-
-	unsigned long flags;
-
-	read_lock_irqsave(&xxx_lock, flags);
-	.. critical section that only reads the info ...
-	read_unlock_irqrestore(&xxx_lock, flags);
-
-	write_lock_irqsave(&xxx_lock, flags);
-	.. read and write exclusive access to the info ...
-	write_unlock_irqrestore(&xxx_lock, flags);
-
-The above kind of lock may be useful for complex data structures like
-linked lists, especially searching for entries without changing the list
-itself.  The read lock allows many concurrent readers.  Anything that
-_changes_ the list will have to get the write lock.
-
-   NOTE! RCU is better for list traversal, but requires careful
-   attention to design detail (see Documentation/RCU/listRCU.txt).
-
-Also, you cannot "upgrade" a read-lock to a write-lock, so if you at _any_
-time need to do any changes (even if you don't do it every time), you have
-to get the write-lock at the very beginning.
-
-   NOTE! We are working hard to remove reader-writer spinlocks in most
-   cases, so please don't add a new one without consensus.  (Instead, see
-   Documentation/RCU/rcu.txt for complete information.)
-
-----
-
-Lesson 3: spinlocks revisited.
-
-The single spin-lock primitives above are by no means the only ones. They
-are the most safe ones, and the ones that work under all circumstances,
-but partly _because_ they are safe they are also fairly slow. They are slower
-than they'd need to be, because they do have to disable interrupts
-(which is just a single instruction on a x86, but it's an expensive one -
-and on other architectures it can be worse).
-
-If you have a case where you have to protect a data structure across
-several CPU's and you want to use spinlocks you can potentially use
-cheaper versions of the spinlocks. IFF you know that the spinlocks are
-never used in interrupt handlers, you can use the non-irq versions:
-
-	spin_lock(&lock);
-	...
-	spin_unlock(&lock);
-
-(and the equivalent read-write versions too, of course). The spinlock will
-guarantee the same kind of exclusive access, and it will be much faster. 
-This is useful if you know that the data in question is only ever
-manipulated from a "process context", ie no interrupts involved. 
-
-The reasons you mustn't use these versions if you have interrupts that
-play with the spinlock is that you can get deadlocks:
-
-	spin_lock(&lock);
-	...
-		<- interrupt comes in:
-			spin_lock(&lock);
-
-where an interrupt tries to lock an already locked variable. This is ok if
-the other interrupt happens on another CPU, but it is _not_ ok if the
-interrupt happens on the same CPU that already holds the lock, because the
-lock will obviously never be released (because the interrupt is waiting
-for the lock, and the lock-holder is interrupted by the interrupt and will
-not continue until the interrupt has been processed). 
-
-(This is also the reason why the irq-versions of the spinlocks only need
-to disable the _local_ interrupts - it's ok to use spinlocks in interrupts
-on other CPU's, because an interrupt on another CPU doesn't interrupt the
-CPU that holds the lock, so the lock-holder can continue and eventually
-releases the lock). 
-
-Note that you can be clever with read-write locks and interrupts. For
-example, if you know that the interrupt only ever gets a read-lock, then
-you can use a non-irq version of read locks everywhere - because they
-don't block on each other (and thus there is no dead-lock wrt interrupts. 
-But when you do the write-lock, you have to use the irq-safe version. 
-
-For an example of being clever with rw-locks, see the "waitqueue_lock" 
-handling in kernel/sched/core.c - nothing ever _changes_ a wait-queue from
-within an interrupt, they only read the queue in order to know whom to
-wake up. So read-locks are safe (which is good: they are very common
-indeed), while write-locks need to protect themselves against interrupts.
-
-		Linus
-
-----
-
-Reference information:
-
-For dynamic initialization, use spin_lock_init() or rwlock_init() as
-appropriate:
-
-   spinlock_t xxx_lock;
-   rwlock_t xxx_rw_lock;
-
-   static int __init xxx_init(void)
-   {
-	spin_lock_init(&xxx_lock);
-	rwlock_init(&xxx_rw_lock);
-	...
-   }
-
-   module_init(xxx_init);
-
-For static initialization, use DEFINE_SPINLOCK() / DEFINE_RWLOCK() or
-__SPIN_LOCK_UNLOCKED() / __RW_LOCK_UNLOCKED() as appropriate.